1. Field of the Invention
The present invention relates to an ignition apparatus for an internal combustion engine which is mounted the internal combustion engine of a vehicle such as an automobile for applying a high voltage to spark plugs to generate spark discharges.
2. Description of the Related Art
In the past, in an ignition apparatus for an internal combustion engine as described in a first patent document (Japanese patent application laid-open No. H 10-22144), a primary coil conductor (referred to as a round conductor) having a round shape in cross section is wound around a primary bobbin. In the case of using this round conductor, the rate of gaps or spaces generated between adjacent portions of the round conductor is high, so the space factor of the primary coil, which is formed of the primary coil conductor wound around the primary bobbin, is low.
In contrast to this, a second patent document (Japanese patent application laid-open No. 2005-150310) discloses a coil conductor which takes a rectangular cross-sectional shape so as to increase the space factor of a coil for reduction in size.
In the ignition apparatus for an internal combustion engine described in the above-mentioned first patent document, the adjacent portions of the round conductor are in line to line contact with each other, so an insulating resin can be easily impregnated between the primary bobbin and the primary coil though the space factor of the primary coil is low.
In contrast to this, if the coil conductor described in the above-mentioned second patent document is applied to the ignition apparatus for an internal combustion engine, there is the following problem. That is, the adjacent portions of the primary coil conductor is in surface to surface contact with each other, so an insulating resin can not be easily impregnated between the primary bobbin and the primary coil, thus generating voids, as a result of which a high voltage is impressed to the voids, generating dielectric breakdown between the primary bobbin and the primary coil.